Thromboembolic diseases including ischemic stroke, coronary heart disease, and venous thromboembolism are the major lethal causes of human beings. Antithrombotic drug therapy is the basic means in the clinical prevention and treatment of thrombotic diseases; however, antithrombotic drugs including fibrinolytic, anticoagulant and antiplatelet agents all have the main and common defects: bleeding tendency and severe hemorrhage risk.
Classic anticoagulants heparins (f.IIa/Xa inhibitors) and coumarins (vitamin K antagonists) were clinically used since the 30s and 40s of the last century and were the cornerstone of therapeutic drugs for deep vein thrombosis, cardiac stroke and postoperative anticoagulant over the past 70-plus years, however, the risk of bleeding and pharmacodynamic/pharmacokinetic defects seriously limited their clinical application. Heparin and coumarin drugs widely inhibit serine protease (coagulation factor) in the clotting cascade, have large individual difference in pharmacodynamics and complex pharmacodynamic-affecting factors, and therefore their clinical application requires to be monitored continuously. For decades, the major approach and one of the goals of anticoagulant development is to improve the selectivity of new drugs for a particular pharmacological target, improve the pharmacodynamic and pharmacokinetic characteristics of the drugs. The studies have made positive progress, among which the most representative is the clinical application of low-molecular-weight heparin (LMWH) such as enoxaparin and oral anticoagulants such as Rivaroxaban and Dabigatran. However, there is still a huge demand in clinic for new anticoagulants with low bleeding tendency.
Fucosylated glycosaminoglycan (FGAG) is a glycosaminoglycan analogue from the body wall or viscera of an echinoderm of Holothuroidea: FGAG has a chondroitin sulfate-like backbone, and the backbone is constituted by sequential connection of disaccharide structural units consisting of hexuronic acid, hexosamine ([→4) D-GlcUA (β1→3) D-GalNAc (β1→]); the backbone chain of FGAG has fucosyl side chains. Generally, it is considered that the sulfated fucoseside chain is linked to D-GlcUAvia a glycosidic bond; both the hydroxyl groups on the backbone chain and side chain of FGAG may have sulfation (Yoshida et. al, Tetrahedron Lett, 1992, 33: 4959-4962; Mourão et. al, J Biol Chem, 1996, 271: 23973-23984).
All native FGAG exhibits significant anticoagulant activity (Mourão et al., Thromb Res, 2001, 102: 167-176; Mourão et. al, J Biol Chem, 1996, 271: 23973-23984) and the anticoagulant activity involves multiple coagulation factor targets, among which the inhibitory activity for the intrinsic factor Xase (f.Xase, Tenase) is the strongest (Sheehan & Walke, Blood, 2006, 107:3876-3882; Buyue & Sheehan, Blood, 2009, 114: 3092-3100). Besides the anticoagulant activity, FGAG also has wide pharmacological activities, such as anti-inflammatory, anti-tumor, fibrinolysis, blood lipid-regulating activity (Tovar et al., Atherosclerosis, 1996, 126:185-195; Kariya et al., J Biochem, 2002, 132(2):335-343; Borsig et al., J Biol Chem, 2007, 282(20): 14984-14991), and shows platelet activation and f.XII activation that are contradictory to its anticoagulant activity (Li et al., Thromb Haemost, 1988, 59(3):435-439; Fonseca et al., Thromb Haemost, 2010, 103(5): 994-1004). The wide pharmacological activities limit the practical application of FGAG.
Structural modification of FGAG is one of approaches to improve its potential application value, for example, preparation of its depolymerized products, the purpose is to decrease the activities of platelet and contact activation, while maintaining the anticoagulant activity. Chinese Patent Publication Nos. CN101724086A and CN101735336A disclose a method for preparing depolymerized fucosylated glycosaminoglycan, wherein the depolymerized product is prepared by peroxide depolymerization that is catalyzed with transition metal ion of the fourth period in an aqueous medium. The product is a potent inhibitor of intrinsic factor Xase, having good anticoagulant and antithrombotic activities, significantly reduces bleeding tendency, and can be used for the prevention and/or treatment of thrombotic diseases. European patents EP 0811635A1 and EP 0408770A1 obtain depolymerized products having a molecular weight of 3,000-80,000 and 3,000-42,000, respectively, by hydrogen peroxide depolymerization of native FGAG. The products can be used in the prevention and treatment of vascular intimal hyperplasia and thrombosis diseases. All of those patent applications employ peroxide depolymerization to obtain depolymerized products of FGAG. The advantage of peroxide depolymerization is that while the molecular weight of the polysaccharide is reduced, the characteristic chemical structure and anticoagulant activity of FGAG can also be well maintained. The disadvantage is that the depolymerization degree of the product is difficult to control, and it is generally required to detect the reaction products by continuous sampling, so as to confirm whether the reaction is complete. Hitherto, the fucosylated glycosaminoglycan derivative having Δ4,5 unsaturated bonds at non-reducing terminal has not been reported yet.